1. Field of the Invention
The present invention relates to an optical pickup suitable for use in an optical disc device for an optical disc such as a compact disc, a magneto-optical disc (such as an MD) or the like.
2. Description of Related Art
A conventional optical pickup employed in an optical disc device is provided with a laser diode, a beam splitter, photodiodes, etc. However, a laser coupler has been applied to the optical pickup as an alternative to the laser diode, the beam splitter, the photodiodes, etc. owing to a demand for a size reduction in the optical pickup and the like.
The laser coupler has an emitting unit for emitting a laser beam to irradiate an optical disc therewith and a receiving unit for receiving therein a laser beam reflected from the optical disc.
This type of laser coupler is a so-called laser-beam emitting device/laser-beam receiving device (hereinafter called a laser-beam receiving and emitting device). The laser-beam emitting and receiving device is incorporated into an IC.
In the conventional laser coupler referred to above, a tracking error signal of the optical disc is obtained by, for example, a so-called push-pull system using one spot. Alternatively, the tracking error signal is obtained by a three-spot system using three spots.
By using the IC incorporating the laser-beam emitting and receiving device therein, the optical pickup can be constructed by a combination of a biaxial device and the IC alone.
The biaxial device is also called a biaxial actuator. In the biaxial device, an objective lens is displaced in focus and tracking directions by a magnetic driving force so as to focus a laser beam emitted from the laser-beam emitting device of the laser coupler onto a signal surface of the optical disc, whereby the laser beam can be accurately applied to a recording track therealong.
The IC having the biaxial device and the laser-beam emitting and receiving device both incorporated therein is provided for a slide base of the optical pickup.
The slide base is used to displace the optical pickup in the radial direction of the optical disc between the inner periphery of the optical disc and the outer periphery thereof.
However, this type of optical pickup needed to prepare the following two adjustments in order to perform the positioning of the laser coupler with respect to the slide base.
Namely, two kinds of laser couplers are needed: one displaced parallel to the slide base to adjust its position according to a tracking mode to be adopted; and the other one rotated relative to the slide base to adjust its position according to the tracking mode to be adopted. It is necessary to move the laser coupler parallel to the slide base to adjust its position or rotatably displace the laser coupler to adjust its position, according to the way of obtaining or adopting tracking.
As the way of adopting the tracking, the push-pull system and the three-spot system are known.
When it is desired to obtain a tracking error signal by the push-pull system, the laser coupler is displaced parallel to the slide base and must be positionally adjusted such that a spot of a laser beam is brought to a proper position of the laser-beam receiving device of the laser coupler.
On the other hand, when it is desired to obtain the tracking error signal by the three-spot system, the laser coupler is rotated and moved relative to the slide base and must be positionally adjusted so that the spot of the laser beam is brought to the proper position of the laser-beam receiving device of the laser coupler.
Thus, since the two types of systems for displacing the laser coupler and adjusting its position are adopted according to the tracking method, it is necessary to prepare two types of different slide bases and two types of different bases for the laser coupler and make varying combinations of the slide bases and the bases for the laser coupler, thus leading to higher manufacturing costs. Further, the parallel-moving type positional adjustment and the rotational-moving type positional adjustment need adjusting jigs much different from each other and adjusting methods of the adjusting jigs are also much different from each other.